Dragon cargo ship attached to space station

Wrapping up a smooth two-day rendezvous, a SpaceX Dragon cargo ship was successfully attached to the International Space Station early Sunday, bringing nearly 5,000 pounds of supplies and equipment to the lab complex.

A SpaceX Dragon cargo ship completed a smooth two-day rendezvous with the International Space Station early Sunday, bringing 2.5 tons of supplies and equipment to the lab complex. (Credit: NASA/Koichi Wakata)

"Capture is complete," Wakata radioed mission control in Houston. "Congratulations to the entire ops team for the successful launch, rendezvous and capture of Dragon. The vehicle, the spacecraft, was very solid and very stable."

"And congratulations to you, Koichi," Jack Fischer replied from the control center. "Great work catching the Dragon. It's been a long road and a lot of hard work by all the team ... to get the Dragon up there and enable the fantastic science that you're about to do next week. So good job to everybody, and thanks for getting her on board."

With the Dragon safely snared, flight controllers, operating the robot arm by remote control, maneuvered the spacecraft to the Earth-facing port of the forward Harmony module where motorized bolts locked it in place just after 10 a.m.

The commercial cargo ship was launched Friday from the Cape Canaveral Air Force Station atop a SpaceX Falcon 9 rocket. This is the third operational flight of a Dragon capsule under a $1.6 billion contract with NASA that calls for at least 12 missions to deliver 44,000 pounds of research gear, station equipment and crew supplies through 2016.

This time around, the spacecraft's cargo included a complete spacesuit, spare parts for suits already aboard the station, food, clothing, a set of legs for the station's humanoid robot, Robonaut2, and research gear, including an experimental laser communications system, high definition video cameras and a mini greenhouse.

The astronauts plan to open hatches to the Dragon capsule early Monday, if not sooner, to unload high-priority science gear. Then they'll turn their attention to preparations for a spacewalk Wednesday by Rick Mastracchio and Steven Swanson to replace an external computer in the station's solar power truss.

The computer, known as MDM EXT-2, is one of two "multiplexer-demultiplexers" used to control a variety of critical systems, including solar array positioning devices and a mobile transporter used to move the robot arm to different worksites on the power truss.

The space station's robot arm moved the Dragon cargo ship to the Earth-facing port of the space station's Harmony module where it was bolted in place to complete a successful rendezvous. (Credit: NASA TV)

MDM EXT-2, operating as a backup to MDM EXT-1, failed April 11 and while the primary computer is working normally, NASA wants to replace the failed processor as soon as possible to restore full redundancy. Mastracchio and Swanson tested a spare MDM late last week and upgraded its software, clearing the way for the spacewalk repair.

While Mastracchio and Swanson are suiting up early Wednesday, the station's Russian crew members will oversee the undocking of a Progress supply ship from the Zvezda command module's aft port. Separation is expected around 4:58 a.m.

The uncrewed supply ship will be maneuvered to a point about 310 miles from the station before it returns for an automated re-docking Friday, testing an upgraded KURS rendezvous navigation system intended for follow-on spacecraft.

With the Progress on its way, Mastracchio and Swanson plan to begin the computer replacement spacewalk around 9:20 a.m. Wednesday. The swap out is expected to take about two-and-a-half hours to complete.

SpaceX is one of two companies hired by NASA to provide space station cargo deliveries in the wake of the shuttle's retirement. The other, Orbital Sciences Corp., holds a $1.9 billion contract for eight resupply missions to carry up 40,000 pounds of cargo and supplies using the company's Antares rocket and Cygnus capsule.

In case of problems with the Dragon flight, NASA had been protecting a May 6 launch target for Orbital's second operational resupply mission. But with the Dragon now safely attached to the station, NASA managers plan to reschedule the Orbital launch for around June 10.